https://play.google.com/store/apps/details?id=com.dictionary
https://play.google.com/store/apps/details?id=com.merriamwebster

maybe see:
https://play.google.com/store/apps/details?id=com.krishnendu.offlinedictionary

seems good:
https://play.google.com/store/apps/details?id=com.duolingo
https://play.google.com/store/apps/details?id=com.duolingo.testcenter&hl=en

https://play.google.com/store/apps/details?id=com.goethe.f50languages&hl=en
https://play.google.com/store/apps/details?id=air.com.rosettastone.mobile.CoursePlayer&hl=en


https://play.google.com/store/apps/details?id=english.grammar.test.app&hl=en
https://play.google.com/store/apps/details?id=com.datnm.englishgrammar

